1. Field of the Invention
This invention generally relates to tools and more particularly relates to machining tools. Most particularly, this invention relates to drills for use with machining centers.
2. Description of the Related Art
Drills are cutting tools that are adapted for use with rotary machines, often referred to as machining centers. A conventional drill includes a body having a shank and a head at the front end of the shank. The head is provided with a cutting edge. A flute extends rearward from the cutting edge along the drill body. The flute is provided for the evacuation of material removed from a work piece by the cutting edge.
In operation, the shank of the drill is supported by a spindle, which is an integral part of the machining center. The spindle is operable to rotate the drill about its central axis. The spindle can be displaced in an axial direction to displace the drill relative to a work piece. Alternatively, the spindle can be axially fixed and the work piece can be displaced in an axial direction relative to the drill. As the spindle or work piece is displaced in an axial direction, the spindle rotates. As the spindle rotates, the cutting edge removes material from the work piece. The material removed is evacuated by the flutes.
Throughout the use of the drill, its cutting edge becomes worn. The cutting edge could eventually become so worn that further use of the drill would be ineffective or inefficient. When this occurs, the worn drill is replaced with a fresh drill.
While the fresh drill is in use, the worn cutting edge can be sharpened for later use. The cutting edge is sharpened by removing material from the head of the drill. Subsequent sharpening operations further remove material from the head of the drill. Ultimately, the length of the drill becomes too short for further sharpening. Consequently, the drill can no longer be used. When this occurs, the drill is reduced to scrap.
To promote a conservation of natural resources and avoid sharpening operations, replaceable inserts have been devised for use with drills. An insert is a generally planar body having a cutting edge. The insert is adapted to be secured in a pocket provided in the head of the drill. Examples of inserts are disclosed in U.S. Pat. No. 4,072,438, to Powers, U.S. Pat. No. 5,340,246, to Tukala, and U.S. Pat. No. 6,019,553, to Yakamavich, Jr.
While cutting inserts are capable of conserving resources and avoiding sharpening operations, the manner in which an insert is secured in a pocket can be inefficient. To solve this inefficiency problem, replaceable tips have been devised for use with drills. A replaceable tip comprises a generally cylindrical body having a cutting edge at its front end. A flute in the tip extending rearward of the cutting edge is adapted to align with a flute in the drill body when the tip is supported by the drill body.
An example of a replaceable tip for use with drills is disclosed in U.S. Pat. No. 6,059,492, to Hecht. This replaceable tip encounters deformation throughout use. The deformation causes the tip and the drill body to become loose relative to one another so that the tip is prone to separate from the body. The tip can become separated from the drill body in the work piece. Extracting the tip from the work piece can be cumbersome if not impossible.
What is needed is a drill that overcomes all of the shortcomings of the aforementioned inserts and tips. In particular, a drill body and a removable drill tip, which do not deform and separate throughout use, are needed.
Generally speaking, the invention is directed toward a drill comprising a drill body and a removable tip. The drill body has a main body portion, a thread, and a reduced diameter portion between the main body portion and the thread. The removable tip has a main body portion and a thread that is adapted to engage the thread of the drill body. One of the threads is an internal thread within a connection bore. The other thread is an external thread extending from a shaft. The internal thread is defined by a front face, a rear face, and a radial surface extending between the front and rear faces. The external thread is also defined by a front face, a rear face, and a radial surface extending between the front and rear faces. The shaft is adapted to be inserted in the connection bore and rotated to engage the internal and external threads with one another.